1. Field of the Invention
The present invention relates to electronic circuits, and more particularly to a low-pass filtering circuit with a variable gain.
2. Description of Related Art
In a number of electronic devices, it is useful to be able to combine a low-pass filter with a variable gain stage, which must provide adequate precision to the gain to be obtained. In general, such a circuit is realized by a series of discrete elements, namely a first filtering element having a fixed gain, followed by one or more amplifier stages, one of which has a variable gain. To realize a variable gain, one frequently uses closed loop amplifier circuits whose back gain is set by discrete values through digital control or variable amplifiers using scale interpolators. A complex combination of components including a series of amplifiers, power sources and more must be provided for all of these circuits.
Such complexity then results in a need for space on the semiconductor product, in an increased power consumption and finally in significantly high implementation costs.
Accordingly, a need exists to overcome the complexity of the prior art and to provide a circuit which is easily to fabricate allowing realization of a low-pass filtering function associated with variable gain.